1. Field of the Invention
The present invention relates to the control of an air conditioner for railway vehicles for maintaining an optimum temperature within the vehicles.
2. Description of the Related Art
Examples of air-cooling railway vehicles using conventional air conditioners will be explained with reference to FIG. 64 schematically showing a train car, the circuit diagrams in FIGS. 65 and 67, the flowcharts of the controlling operation in FIGS. 66 and 68, and FIGS. 69 to 71 schematically showing the concepts of the controlling operation.
FIG. 64 is a schematic view of the structure of a train car equipped with a conventional air conditioner and the flow of data therewithin. This is similar to the structure of a train car equipped with an air conditioner and the flow of data therewithin described in Japanese Utility Model Laid-Open No. Hei 2-41037. In FIG. 64, the reference numeral 1 denotes a train car, 2 an air conditioner mounted on the upper part of the train car 1, 3 a heating/cooling power controller for controlling the heating/cooling power by varying the power of a compressor provided in the air conditioner 2, 4 an air conditioner control unit having a means for determining the heating/cooling power, 5 a control switch portion by which a train operator selects the heating or cooling operation, ON or OFF and sets the target temperature in the car, 6 a temperature detector which is composed of a thermistor or the like so as to detect the temperature of the air returned from the car, 7 a heated/cooled air supply opening and 8 a suction opening for sucking the air from the car.
FIG. 65 is a circuit diagram of the air conditioner 4. The air conditioner 4 is composed of an input circuit 41, a CPU 42, a memory 43 and an output circuit 44. An output from the control switch portion 5 in the train operator's compartment and an output from the temperature detector 6 are input to the input circuit 41. The heating/cooling power controller 3 controls the power of the compressor in accordance with the output of the output circuit 44. The CPU 42 calculates the optimum heating/cooling power, and the result of the calculation is supplied to the output circuit 44.
The operation of the air conditioner 4 will now be explained with reference to FIG. 66. A conventional air cooling device of this type controls the air temperature so as to be the target temperature or in the vicinity thereof while calculating the optimum cooling power from the difference between the temperature of the air to be controlled and the target temperature. This control method is generally called proportional control.
The proportional control method will be explained in the following with reference to the flowchart in FIG. 66. At step F1, the air conditioner 4 of the train is first turned ON by a train operator, and the target temperature T0 is set at step F2. At step F3, a preset time for measuring the temperature is allowed to pass, and the air temperature Tn in the car is detected at step F4. The temperature difference dT between the target temperature T0 and the air temperature Ta in the car is obtained at step F5. At step F6, the optimum cooling power is newly calculated from the temperature difference dT, in accordance with the cooling power chart shown in FIG. 69. When the optimum cooling power is obtained in this way, the cooling power for the current cooling operation is changed at step F7, and the cooling operation is continued at the newly changed cooling power at step F8.
In such proportional control, however, since the cooling operation is conducted at the cooling power determined by the temperature difference between the temperature of the air to be controlled and the target temperature, it is difficult to reach the target temperature depending upon the condition of the load, as shown in FIG. 70 which shows the concept of the controlling operation. For example, even if the cooling power is reduced, the air temperature in the car is sometimes lowered to a temperature lower than the target temperature after the time t1.
To solve this problem, PID control is disclosed in Japanese Utility Model Laid-Open No. Hei 2-41037. In PID control, not only is the temperature difference between the temperature of the air to be controlled and the target temperature detected, but also the precedent temperature difference is stored, and the optimum cooling power is calculated from the detected temperature difference and the precedent temperature difference. Therefore, the air temperature in the car does not remain at a different temperature from the target temperature for a long time but is easily controlled to be the target temperature. However, the air temperature in the car is susceptible to a change in the load such as the outside air temperature and the number of passengers, and it is difficult to follow the change in the load which occurs in a short time such as the increase in the amount of ventilating air due to the opening and closing of the doors and the passengers getting on and off. In addition, PID control is disadvantageous in that the calculation is complicated and in that a large memory capacity is required.
In the control method shown by the circuit diagram in FIG. 67 and the flowchart shown in FIG. 68, a fuzzy theory is applied to the control of the air conditioner so as to enable simple control and the attainment of the target temperature. The electric circuit shown in FIG. 67 has a region 431 of the memory 43 for storing a previously measured temperature difference dT.
This control method will be explained with reference to the flowchart in FIG. 68. The air conditioner of the train is first turned on by a train operator or the like at step F11, and the target temperature is set at step F12. At step F13, a preset time for measuring the temperature is allowed to pass, and the air temperature in the car is detected at step F14. The temperature difference dT between the target temperature and the air temperature in the car is obtained at step F15. At step F16, judgement is made as to whether or not the current measurement is a first measurement. If this is a first measurement, this temperature difference is stored in the memory 43 as a precedent temperature difference dTs. On the other hand, if this is a second or later measurement, the variance St of temperature difference with time, which is the difference between the precedent temperature difference dTs and the current temperature difference dT, is obtained at step F17. It is possible to determine whether the temperature in the car is stable or has changed in a short time from the variance of temperature difference with time. At step F18, the optimum cooling power is calculated by applying the fuzzy theory. FIG. 71 shows the image of the fuzzy rule. As shown in FIG. 71, the optimum cooling power for making the temperature in the car equal to the target temperature is inferred from the temperature difference dT between the air temperature in the car and the target temperature, and the variance St of temperature difference with time. For example, if the temperature in the car is lower than both the target temperature and the previously measured temperature, it is judged that the air-cooling is excessive, and the cooling power is reduced. On the other hand, if the temperature in the car is higher than both the target temperature and the previously measured temperature, it is judged that the air-cooling is insufficient, and the cooling power is increased. If there is no temperature difference between the air temperature in the car and the target temperature and there is no difference in the current temperature change and the precedent temperature change, it is judged that the air temperature in the car is being maintained in a good state and the cooling power is maintained as it is. When a correction value for the cooling power is obtained in this way, the cooling power for the current cooling operation is corrected by the correction value at step F18, and the cooling operation is continued at the newly changed cooling power at step F20. The temperature difference dT between the target temperature and the air temperature in the car is stored in the memory 43 as a precedent temperature difference dTs, and there is then a pause until the next temperature detection takes place.
Since the cooling operation is conducted while determining the correction value in accordance with the temperature in the car and the temperature change in this way, the temperature in the car is never maintained at a different temperature from the target temperature for very long and it is possible to follow well the change in the load. In addition, since the amount of data stored in the memory 43 need only be a precedent temperature difference, it is possible to control the cooling power relatively simply.
As explained in the related art, in a conventional air conditioner, the heating/cooling operation is conducted while changing the heating/cooling power to the optimum value using the correction value inferred from the temperature difference between the temperature in the car and the target temperature and the variance of temperature difference with time in accordance with the fuzzy rule so that the temperature in the car is constantly comfortable for the passengers. One of the important factors to be taken into consideration in determining the heating/cooling power is the load of the heating/cooling system. The load of the heating/cooling system thermally influences the space being heated or cooled. It is, for example, the outside air temperature which influences the air temperature in the car due to ventilation or by heat transferred from the wall, and passengers who evolve heat in the car. In the case of railway vehicles which run a long distance, the outside air temperature changes momentarily. In the case of subways, the platforms of some stations are air-conditioned, and the outside air temperature is different when traveling through tunnels than while stopping at stations. Since the railway vehicles have a number of large windows, the influence of solar radiation through the windows is large in all vehicles except subway trains, and its influence changes greatly according to the direction of travel and when vehicles run through tunnels. In addition, a great many passengers get off and on every time a train reaches a station, and sometimes, a car is heavily crowded in a certain section while there are few passengers in other next sections.
Since the heat evolved by the passengers greatly influences the heating/cooling operation, if the number of passengers is rapidly reduced, the temperature in the car is lowered, while if the number of passengers is rapidly increased, the temperature in the car is raised, Simultaneously with passengers getting off and on, a large amount of air ventilates, and the air temperature in the car changes due to the influence of the outside air temperature. It can be said that a typical characteristic of the air-conditioning in railway vehicles is that the load constantly changes in this way. When the load is large, even if the temperature change and the difference between the temperature difference and the precedent temperature difference are the same as in the case of a small load, it cannot be said that the temperature in the car will be changed in the same way by the same correction value for the cooling power. The outside air temperature will be cited as an example of the load of the cooling system. When the outside temperature is high, since a large amount of heat transfers to the inside of the car through the wall and hot air enters the inside of the car due to drafts or by ventilation, the temperature in the car is difficult to lower by increasing the cooling power in the same way as in the case of a lower outside air temperature and, if the cooling power is reduced, the temperature in the car rises in a short time. On the other hand, if the outside air temperature is low, even with a little increase in the cooling power, the temperature in the car is easily lowered and, even if the cooling power is reduced, the temperature in the car is not raised so much. The same may be said of the amount of radiant heat by solar radiation or the like and the number of passengers. In this way, the state of the ambient load exerts great influence on the operation of the air conditioner. In such cases, it is impossible to calculate the correction value with due consideration of the load by a conventional calculation method. As a result, it is impossible to follow the change in the load and the temperature in the car disadvantageously becomes too low or too high.
In the above-described control methods, control is carried out on the assumption that the temperature in the car is kept constant. The human thermesthesia, however, is not determined merely by the air temperature but it is determined by the amount of heat produced within the human body and the amount of heat dissipated to the outside of the human body. If the amount of dissipated heat is large, a human being feels cold, while if it is small, he feels hot. The amount of dissipated heat is determined by temperature, radiation, air flow, humidity, etc. For example, if the outside air temperature is high, the amount of heat dissipated to the outside of the human body is reduced, and the human being feels hot, while if the outside air temperature is low, the amount of heat dissipated to the outside of the human body is increased, and the human being feels cold. As to radiation, if there is warm heat radiation, the amount of heat dissipated to the outside of the human body is reduced, while if there is cold heat radiation, the amount of heat dissipated to the outside of the human body is increased. As to air flow, if a large amount of wind blows against the human body, the heat on the surface of the human body is lost and the amount of heat dissipated to the outside of the human body is increased, while if the amount of wind is small, the amount of dissipated heat is reduced. In dissipating heat, a human being dissipates water out of the human body. If the balance between the amount of heat produced in the human body and the amount of dissipated heat is lost, the human being perspires in order to dissipate more heat. When the perspiration is evaporated, the heat on the surface of the human body is lost, thereby increasing the amount of dissipated heat and controlling the body temperature. However, if the ambient humidity is high, perspiration is unlikely to evaporate, and the amount of heat dissipated from the human body is reduced, so that the human being feels hot. In this way, temperature, radiation, air flow, humidity, etc. play an important role in the human thermesthesia. In heating or cooling a certain space, the temperature difference between the upper portion and the lower portion must be particularly take into consideration. The human thermesthesia is said to be determined by the temperature at his feet. Even if the temperature at the upper half of the body is high, if the temperature at his feet is low, the human being feels cold. On the other hand, even if the temperature at the upper half of the body is comparatively low, if the temperature at his feet is high, the human being feels warm. In heating or cooling a car, since the doors are opened when the train reaches a station and a large amount of ventilating air flows, the temperature in the car is unlikely to become stable. When a great number of passengers are in the car as in a commuter train, the air is unlikely to flow vertically in the car. For these reasons, a temperature difference is apt to arise between the upper portion and the lower portion. It is therefore important to heat or cool the car in due consideration of the temperature difference between the upper portion and the lower portion of the car.
In conventional control methods, however, the heating/cooling operation is carried out so that the temperature in the car is kept constant, so that the human thermesthesia changes with a change in the radiation, air flow or the temperature change between the upper portion and the lower portion of the car. The passengers therefore feel unfavorably hot or cold in spite of the target temperature.